Mitochondria can be bad dance partners. So bad, in fact, that they can cause male sterility – in plants at least.
Studying the causes and effects of mitochondria and chloroplast misconduct is the theme of two research grants recently awarded to Colorado State University Assistant Professor of Biology Dan Sloan in the College of Natural Sciences. One grant of $1.55 million over five years was awarded by the National Institutes of Health in September. The other award of $676,000 over four years was granted by the National Science Foundationin July.
Genomes out of sync
We might think of our cells as all under the direction of a single set of DNA. But mitochondria – and, in plants, chloroplasts – actually contain their own sets of DNA that operate separately from the DNA bound up in the cell’s nucleus. With support from both grants, Sloan will study interactions between plant cells’ nuclear genomes and the genomes of those cells’ mitochondria and chloroplasts. Interactions between the genomes of these organelles are intimate and complex, much like dance partners, Sloan said.
“The basic biological functions that organisms have to carry out is dependent on multiple different genomes,” he said. “They all have to play nice with each other for the cell to work.”
In particular, Sloan’s research will try to understand what happens when the genome of one organelle changes faster than others.
“We want to know, when one changes, how does that affect those interactions?” he said.
Because mitochondria and chloroplasts have their own genomes, they can mutate independently of the DNA in a cell’s nucleus. The mitochondrial mutation rate is low in most plants, but high in humans and other animals, where it is linked to diseases such as diabetes, Parkinson’s and cancer.
With support from the National Institutes of Health, Sloan and his team are interested in how most plants have been able to decrease their mitochondrial and chloroplast mutation rates. “We will use techniques to measure new mutations as they occur in plant mitochondria and chloroplasts to better understand how they maintain such incredibly low mutation rates,” Sloan said.
The answers could help us understand how mitochondria can get out of step with the rest of a cell’s DNA – and how to prevent diseases in people.
Nucleus arms race
In some plants, mutations of mitochondria and chloroplast genomes can cause the male parts of the plant to become sterile. Sloan said this benefits the mitochondria and chloroplast because they pass on their genomes through the female parts of the plant. However, it doesn’t allow the nucleus to transmit all of its genetic material.
“It’s like an arms race with the nucleus,” he said.
He will study this potential arms race by taking chloroplast genes out of flowering plants from the Silenegenus – a group found within the “pink” or “carnation” family – and inserting them into tobacco plants. Unlike most plants, Silene species have an extremely high rate of mutation in their mitochondria and chloroplast genomes, Sloan said. And because tobacco chloroplast genomes are easy to modify, the team will be able to implant Silene chloroplast genes and create new combinations of genes within tobacco cells. Then they will study how disrupting basic interactions between genomes affects the whole plant.
For this particular investigation, funded by the National Science Foundation grant, Sloan will work with a team in the Department of Biology that includes Salah Abdel-Ghany, a special assistant professor of biology, Amanda Broz, a genetic research scientist, Alissa Williams, a cell and molecular biology Ph.D. student, and multiple CSU undergrads.
With the National Institutes of Health grant, Sloan will work with Zhiqiang Wu, a former CSU postdoctoral fellow now at Iowa State University, and CSU undergrads.
